These are more frequent

Jean GorvettPond Life, Ill. Paxton Chadwick, Londres, Puffin Picture Book n° 93, (1952), 1958, p. 14.

These are more frequent in streams. You may come across a caddis worm with a neat little case made of small pieces of leaf. It can swim actively with its long legs. All the case-building caddises keep up a flow of water over their gills by wriggling their bodies the whole time.